In a semiconductor integrated circuit, there is a case where a device having negative differential resistance is required. Similarly to another active device, also in such a negative resistance device, it is, of course, desirable that the device operates at a lower voltage and operates at a high speed (high-frequency characteristic is excellent), and various researches have been carried out until now.
However, that there is no control terminal is, in itself, liable to become a problem, there is a limit in control from outside, and it can be unsuitable for application to a logical device or as an integrated device. Besides, an amplifying function or the like cannot be naturally expected. Accordingly, after all, a negative resistance device having a three-terminal structure including at least a control terminal is required, and under the premise, as a future tendency, it appears that primary importance is attached to the realization of a low voltage operation, a high output and a high PVCR.
As one countermeasure against that, hitherto, there is proposed a structure in which a compound heterojunction structure is used, a layer portion having a relatively narrow energy band gap and a high mobility is made a main transit channel for electrons, and a layer portion having a relatively wide energy band gap and a low mobility is provided as a second channel to come in contact with this (see, for example, non-patent document 1). Alternatively, there is a trial in which delta doping is applied to only one of double channels of the same material, and negative resistance is realized by a difference in the mobility (see, for example, non-patent document 2).
In a low dimensional field effect device having the dual-channel structure as stated above, a transit electron (hot carrier) that is accelerated by a drain voltage and reaches the energy level of a potential barrier between both the channels is real-space transferred to a low-mobility channel sandwiched between the gate and the main high-mobility channel by applying a positive gate voltage. The electron transferred to the low-mobility channel is decelerated and transits or is stopped, and as a result, the planar density of electrons passing through the high-mobility channel is obtained by subtracting the electric charge accumulated in the low-mobility channel from the total amount of electric charge induced to satisfy a charge neutrality condition by the gate voltage. The same effect as biasing the gate bias by the amount in the negative direction is produced, and electrons in the high-mobility channel are reduced so that the drain current is substantially decreased, and the negative differential resistance occurs.
On the other hand, part of the present inventors has already proposed that in order to realize such principle, a dual-channel field effect device structure using a quantum wire for the high-mobility channel is advantageous to suppress scattering of carriers in the channel (see patent document 1). Further, in order to obtain this quantum wire, there is also proposed a method in which the quantum wire with a very small width and very small thickness can be formed without being limited by normal lithography (see patent document 2). Besides, there is proposed that a higher PVCR can be obtained by forming a quantum wire and a quantum well in the same process (see patent document 3).
Further, non-patent document 3 discloses a report example in which a high-mobility quantum well layer and a quantum dot are made adjacent to each other and negative resistance is observed.
Non-patent document 1: “Enhanced Resonant Tunneling Real-Space Transfer in delta-Doped GaAs/InGaAs Gated Dual-Channel Transistors Grown by MOCVD”, Chang-Luen Wu et al., IEEE Transactions on Electron Devices vol. 43 No. 2 (1996) 207)
Non-patent document 2: “Gigantic negative transconductance and mobility modulation in a double-quantum-well structure via gate-controlled resonant coupling”, Y Ohno et al., Appl. Phys. Lett. vol. 62 No. 16 (1993) 1952.
Non-patent document 3: J. Phillips et al., “Characteristics of InAs/AlGaAs self-organized quantum dot modulation doped field effect transistors”, Appl. Phys. Lett. Vol. 72, No. 26, 3509-3511 (29 Jun. 1998)
Patent document 1: JP-A-2001-185559
Patent document 2: JP-A-2002-299637
Patent document 3: JP-A-2004-349538